A mysterious and long-disputed document purported to be America’s oldest surviving manuscript is genuine.

That’s the conclusion of a new review of research on the Grolier Codex, a fragmentary 13th Century Maya text whose unlikely provenance ― it was reportedly found by looters in a Mexican cave in the 1960s ― had led some to conclude that it was likely a forgery.

“With this review, which examines information that a forger in the early 1960s could not possibly have known, it becomes crystal clear that this is the earliest surviving book in the New World,” Dr. Stephen Houston, a Brown University archaeologist and a member of the team that conducted the review.

As described recently in a paper published in Maya Archaeology, the team reached their conclusion after an exhaustive analysis of existing research on the codex (the term is used to describe a manuscript in book form).